Trastuzumab is a targeted therapy used in HER2-positive breast and gastric cancers. It is often used in patients whose tumors overexpress the HER2 protein.

It belongs to a class of drugs known as monoclonal antibodies.

Trastuzumab works by binding specifically to the HER2 receptor on the surface of cancer cells. This may block growth signals and also help the immune system recognize and destroy these cancer cells.

While it is designed to target cancer cells, some normal cells that express HER2 may also be affected, and monitoring, particularly of heart function, is often recommended during treatment.